The present invention relates to airbags for reducing an impact of passengers or occupants against interior vehicle components in the event of side collision of motor vehicles.
Recently, airbag systems come into wide use as passenger restraint systems, and are available for various seat positions such as driver's seat, assistant driver's seat and rear seat to cope with not only frontal collision, but side collision of motor vehicles. Particularly, airbags for reducing an impact of passengers in the event of side collision (refer hereafter to as side airbags) receive attention as means for increasing the security of passengers.
However, as being deployed in a narrow space between a passenger's seat and a vehicle body, the side airbags need to restrain passengers with small shape and volume thereof. Thus, it is necessary to avoid raising a problem that unnecessarily expanded airbags upon deployment disable full absorption of an impact energy of passengers, or come in contact with the passengers to provide an impact to them.
The side airbags or inflatable curtains deploy along a side window and cover the whole or part thereof to prevent passengers from strongly colliding with the side window and the neighborhood thereof. In order to cover the passenger's head even if the vehicle body rolls due to a side-collision impact, the inflatable curtain needs to have high airtightness to such an extent that no gas leakage occurs from a bag over a few seconds after deployment. Thus, a bag fabric or cloth for the inflatable curtain is coated with silicone resin or rubber.
With the inflatable curtain accommodated in the vehicle body on the periphery of the side window, an extremely narrow accommodation space of a pillar and a roof side requires a reduction in bulk and sectional area of a folded bag. If the bag is designed to use a fabric for an earlier-art driver's seat or assistant driver's seat airbag, the accommodation of the folded bag requires partial alteration of the vehicle-body structure design or arrangement of a separate and distinct accommodation unit.
JP-A 10-129380 discloses a joining method of an outer periphery of a side airbag using a fabric coated with silicone rubber, wherein a sewed portion is sealed with a sealing member to increase the airtightness. This method provides an airbag with very tough outer periphery for higher airtightness, which is apt, however, to be rough and hard, and is difficult to reduce a folded volume.
JP-A 2-114035 discloses an airbag fabric having improved airtightness by laminating thermoplastic elastomer. According to a type of thermoplastic elastomer, the fabric may cause adhesion between fabric portions or lack of heat resistance to hot gas out of an inflator after leaving the airbag folded during a long period of time.
JP-A 11-227550 discloses a bonded airbag wherein the periphery of a fabric coated with silicone rubber is joined with a hot-setting silicon-rubber adhesive to have a junction peeling bonding strength of 150 N/25 mm width or more. In order to obtain a predetermined bonding strength, this art relies upon 1) introducing a coating rubber into a texture of the fabric, and 2) enhancing cross-linking and chemical bond between the fabric and a coating layer and between the coating layer and an adhesive by using a specific rubber mixing compound. However, the cured coating rubber and adhesive make the periphery of the fabric significantly rough and hard, scarcely securing a reduced folded volume to be achieved by the present invention.
JP-A 2001-1854 discloses an airbag wherein two panels are joined with thread sewing and a resilient adhesive having 200% or more fractural elongation so as to prevent a gas leakage from a sewed portion of the panels. This airbag provides greater fractural elongation, but cannot satisfy the requirements for endurance characteristics.
U.S. Pat. No. 5,482,317 discloses an inflatable protective cushion using a fabric of nylon 66 of 50-155 dtex. The weight of the fabric is half or less an earlier-art airbag fabric, which is superior in the earlier -art level in view of a weight reduction, but inferior therein due to lack of mechanical characteristics of the fabric itself. This cushion is of a rectangular outer peripheral shape to remove sewing on the outer periphery and thus secure the pressure tightness of the cushion. It is difficult, however, to apply the cushion to complicatedly shaped bags such as side airbag.